Introduction

The new Pentax SMC-DA* 50-135mm f/2.8 ED [IF] SDM is an urgently needed addition to
the line-up - till its release the low-end DA 50-200mm f/4-5.6 ED
was the only current production tele zoom lens by Pentax. It is a dedicated APS-C lens
with a field-of-view equivalent to 75-203mm on full format cameras so it is obviously
meant as a revival of the classic 70-200mm f/2.8 medium tele zooms. The optical
design is the result of a co-development with Tokina whereas the mechanical implementation
is different.

The 50-135mm is a member of the professional grade DA* family and the build quality
is on an accordingly high level thanks to quality materials and weather-sealing.
Unlike Tokina Pentax decided not to implement a tripod collar - this a bit of
a borderline approach but a viable one regarding the comparatively moderate weight (685g).
The physical length of the lens remains constant regardless of the zoom or
focusing action. The broad, rubberized zoom ring operates very smooth.
Thanks to an internal focusing system (IF) the front element
does not rotate so using a polarizer is no problem. The Pentax Super Protect (SP)
coating on the front element has been optimized to repel dust, water and grease.

The DA* 50-135mm f/2.8 features a new Supersonic Dynamic Motor (SDM) AF (*)
although it also offers the old AF drive screw for legacy DSLR support. In terms
of technology the Pentax SDM is pretty much comparable to Canon's USM or Nikon's SWM -
ultrasonic motors operate near silent and usually a bit faster than conventional
AF motors. That said the 50-135mm doesn't really live in a league of its own speed-wise -
it's certainly fast enough though. Thanks to a Quick-Shift system manual focus
override is instantly possible in Single-Shot AF mode once the focus has been achieved.
The AF accuracy of the tested sample was spot on when approaching the focus point from
longer focus distances, less so from closer distances.

(*) In order to take advantage of the SDM drive you need to upgrade a Pentax K10D to
firmware v1.30.